As a new generation of wireless communication system, a Long Term Evolution (LTE) system is increasingly gaining popularity in more and more countries and states. As compared with second generation mobile communication (2G) and third generation mobile communication (3G) systems, the LTE system can provide a higher data transmission rate, and a Multiple-Input Multiple-Output (MIMO) technology is deemed as a core technology of the LTE system and also attracts more and more attention of designers.
The MIMO technology is a space diversity technology by a multi-transmit and multi-receive antennas, which uses a discrete multi-antenna mode, so it can effectively decompose a communication link into a plurality of parallel sub-channels, so as to significantly improve channel capacity, and further improve the data transmission rate of the system. The MIMO technology typically requires multiple antennas to support multiple input and multiple output. In consideration of actual situations and space limitations of a mobile terminal, a mobile terminal is generally provided with two antennas to constitute a MIMO antenna system. One antenna supports input and output at the same time, which is referred as a main diversity antenna. The other antenna generally supports input only, which is referred as a diversity antenna. In order to ensure good performance of the MIMO system, the two antennas not only needs to have a higher efficiency, but also needs to have a lower correlation between the two antennas.
Since there is limited space for accommodating the antennas in the mobile terminal, for example in a low frequency band of 700-960 MHz, a distance between the two antennas is small with respect to a wavelength, a near-field coupling between the two antennas is strong, and respective efficiencies thereof are relatively low. Thus, the MIMO antenna system of a mobile terminal exhibits a poor performance in the low frequency band.